Microwave generator



July 1, 1952 U 2,602,146

MICROWAVE GENERATOR 2 SHEETS -SHEET 1 Filed Sept. 25, 1946 F. LUDI MICROWAVE GENERATOR Jl lly 1, 1952 2 SHEETSSHEET 2 Filed Sept. 25, .1946

constructions. invention are to provide microwave -generators including hollow cavity resonators with elec-v Patented July 1, 1952 Fritz Liidi, Baden, Switzerland,

Patelhold .Patentverwertung assignor to & Elektro- Holding A.-G., Glarus, Switzerland "Application September 25, 1946, Serial No. 699,134 In Switzerland September 1, 1942 Section 1, Public Law 690,

Patent expires September 1,

August 8, 1945' 17 Claims. 01. 315-) 1 This invention relates to microwave generators of. the hollow cavity resonator type in which the oscillatory voltage is developed through the density modulation of an electron beam.

In apparatus of this general type, electrons ofinitially'homogeneous velocity are subjected, to an alternating current field of ultra high frequency and thus modulated as regards their velocity so that more or lessdefinite groups of electrons are formed a certain distance away from the modulator, these electron groups then developing alternating voltages in an inductor. Some of the known microwave generators of this hollow cavity resonator type have a poor transit. time so that the alternating voltages of the res-' onator oscillations must be relatively large to prevent the efficiency from dropping below a cer-' tain value, and in other known generators the energy absorbing grids are not located at points between which the developed oscillatory voltages are a maximum, so that also in this case the maximum efliciency is not obtained.

Objects of the present invention are to provide microwave generators which avoid the'disadvantages of the prior devices and operate with relatively high efficiency. An object is to provide a microwave generator of the hollow cavity resonatortype in which the voltage maximum of the electrical oscillations is set up at only one region of the resonator cavity when oscillation at thefundamental frequency of the cavity is'estab lished. An object is to provide a resonator-"cavity type of microwave generator in which the feedback factor is less than unity and can be established at practically any desired value by the relative location of the control electrodes with respect to a Wall of the cavity. An object is to provide a resonator cavity type of microwave generator in which the control grid and energy absorbing electrodes form parts of walls of-the resonator cavity, whereby currents may flow to them from all directions and thus elimimate the losses which arose from the heating of theelectrode leads which were essential'in'prior More specifically, objects of the trodes for developing oscillations through the phase-focusing of electrons, and in which" at least one electron beam penetrates, in succession, two control electrodes and two energy ab-- sorbing electrodes.

These and other objects and the advantages of the invention will be apparent from the followin specification when taken with the accompanying drawings, in which:

Fig. 1 is a perspective View, with parts broken away,'of a hollow resonator cavity embodying the,

invention; 7

Figs-2,3 and i are perspective views of other forms of resonator cavities embodying the invention;

away, ity'resonator of the type illustrated in Fig. l;

Sis a perspective view, with parts broken Fig- 6 is a similar perspective view of a microwave generator including a; cavity resonator of the type illustrated in Fig. 2; and

Fig. 7 is a perspective view, 'as vertical section,'of another embodiment in which the" hollow cavity resonator, and associated elements constitute'the major portion ofcthe envelope of the tube.

In Fig. 1 the reference numerals I, 2 identify the approaching'and exit portions, respectively, of an electron beam of initially homogeneous composition'which passes downwardly through an elongated hollow cavity resonator 3 whichis closed at both ends, .and preferably, as is of rectangularcross-section. The corners of the parallelepiped may be rounded off, or an elliptical or circular cross-section may be employed, but the rectangular cross-section is the presently preferred construction. Assuming that the path of theelectron beam is deflected through by a magnetic field, as will be described later, the electron beam may again penetrate the cavity resonator 3;;the portion 4 of the reverseddirection beam passing upwardly through the cav-' ity resonator to emerge as the beam section 5. Control electrodes 6, 6 are arranged at or in the planes oi the upper and lower walls of the resonatorin the. path of the beam section i, and energyabsorbing grids 1, I are similarly arranged at'orin'the planes of the upper and lower walls at ap-' proximately the center of the resonator and in the path of the beam section 4.

When oscillations are generated in the reso -i nator 3,'the electrons of the. substantially ho-" mogeneous beam section I are velocity-moduof 'a-microwave generator including a cavseen in central illustrated,

lated by the alternating electrical field between the control electrodes 6, 6, so that phase-focusing occurs in the section 2 of the beam. The electrical oscillations within the resonator 3 are amplified by the passage of the non-homogeneous section 4 of the beam through the resonator provided, of course, that the travel of the bunched groups of electrons and the alternating electrical fields at the energy-absorbing grids T, I

. are properly related. It is not necessary to provide special means for initiating oscillations in the hollow cavity resonator as accidental inhomogeneities in the entrance beam section I will set up oscillations. With the horizontal edges designated A and B respectively, and the vertical edges designated C, as shown in Fig. 1, the electrical field strengthone) There is a voltage antinode at the center of the resonator when oscillations are set up at the fundamental frequency, and therefore a maximum alternating effect exists between the phasefocused beam and the electrical field at the energy-absorbing electrodes 1. The control electrodes 8, 6 are located in the vicinity of one of the endwalls ac, i. e. in a region where the electrical field strength is small, whereby the feedback factor is less than unity; and it is essential that this condition be fulfilled if maximum efficiency is to be obtained. The degree of .feedback may be preselected at a desired value by an appropriate selection of the spacing of the control electrodes from the end wall or may be. adjusted by providing means, similar to those disclosed hereinafter for varying the volume of the resonator cavity, for varying the spacing of the control electrodes from the end wall.

It'is possible, by an appropriate shaping of the elongated hollow cavity resonator, to eliminate the magnetic field system which must be employed to reverse the direction of the beam with a cavity resonator as shown in Fig. 1. A ringshaped resonator 3a permits the location of the sets of control electrodes 6 and energy-absorbing electrodes 1 in a straight line, see Fig. 2. The ring resonator 3a may be assumed to be constructed from the right parallelepiped cavity 3 of Fig. '1 by bending the latter to bring the end surfaces ac into engagement with each other. The wall 8 which extends radially across the annulus 3a of rectangular cross-section provides a common wall A C for the opposite ends of the cavity resonator. .This partition wall 8 is located adjacent the control electrodes 6, and therefore at some distance from the energy-absorbing. electrodes I. The type of oscillations is the same as with the Fig l construction and, since the same conditions as to maximum and minimum electrical field strength apply to the ring resonator of Fig. 2, the feedback factor is lessthan unity as the electrical field in the region of thecontrol electrodes 6 is smaller than the electrical field in the energy-absorbing electrodes 1.

Another modification to locate the modulator and inductor elements of the resonator in a straight line is shown in Fig. 3. This J -shaped form of the resonator 322 may be viewed as developed from the Fig. 1 resonator by bending one end portion of the resonator to bring the axis of the beam path through the electrodes 6 into coincidence with the axis of the energy-absorbing electrodes 1. The operating characteristics of this form of the invention are substantially identical with those of the previously described constructions.

A further constructional arrangement for eliminating the magnetic field system of the Fig. 1' embodiment is illustrated in Fig. 4. An auxiliary resonator 9 is arranged below the resonator 3 andv excited by the electron beam I, 2 which penetrates the control electrodes 6 of the resonator 3 and electrodes [0 of the resonator 9, and a second electron beam 1 I of initially homogeneous composition passes upwardly through the electrodes l2 of resonator 9 and the energyabsorbing electrodes 1 of the resonator 3.

The fundamental frequency may be varied by alteringthe volume of the frequency-determining hollow space at points where the magnetic or electrical fields are strongest. Such an adjustment may be obtained if the wall of the respnator is flexible and a pressure screw is provided, or if a metal piston is mounted for adjustment to penetrate into the hollow space to an adjustable extent. The first arrangement, as illustrated in Fig. 2, comprises a bracket I3 mounted on the resonator 3a and having a bushing through which a screw [4 is threaded to contact a flexible portion of the circumferential wall of the resonator. The adjustable piston construction for controlling the fundamental frequency will be described later.

Various arrangements for'the mounting of the hollow cavity resonators and associated elements of a micro-wave generator Within an evacuated envelope are of course possible. As shown somewhat'schematically in Fig. 5, a resonator 3 of the right parallelepiped type is mounted by one or more'struts [5 within an evacuated envelope [6. Anelectron gun assembly comprising a hot cathode l7 and focusing electrode (-8 establishes the electron beam l which is accelerated by a collecting electrode H! which is maintained at a positive potential. The direction of the beam is reversed after its first passage through'the resonator 3 by a magnetic field structure comprising a yoke 20 and winding 2|. An output loop 22 extends into the resonator cavity and is suitably mounted in and supported by the envelope l6.

A ring-shaped resonator 3o such as shown in Fig. 2 may be supported within a glass envelope 23.by means of metal plates or tabs 24 soldered to opposite sides of the resonator and to supporting rods or Wires 25, see Fig. 6. The electron gun assembly l1, It may be substantially identical with that illustrated in Fig. 5. A collecting electrode 26 of disk form is supported in alinement with the electron gun and the electrodes of the resonator by a rod or wire 27. 22' penetrates the resonator cavity and is supported by a tubular extension 23 of the envelope.

In an all-metal tubeconstruction, as shown in Fig. 7, the envelope is formed by the parallel walls 28 of circular form and the outer cylindrical wall 29 of the resonator 3b. The resonator is completed by the inner cylindrical wall 30 and the radial wall 8 which is adjacent the control A coupling 'loop electrodes 6, 6. A dome 3| jextends above the ou'terwall 29 and may serve as the collectin electrode ora'separate collecting electrode may be supported within and insulated from the dome and envelope. The-electron gun assembly 11, I8 is mounted in a glass or ceramic'cup 32-whichis unitedto a short cylindrical sleeve or bushing, 33 welded to the outer wall'29;

The fundamental frequency may be altered by a metal piston 34 which is sealed within the tube by a corrugated flexible sleeve 35, and is mounted on a shaft 36 which is threaded through the end wall of a metal cap 31 soldered or welded to a side wall 28 of the tube. A knob 38 for manual adjustment of the piston 34 is secured to the end of the shaft 36. In this constructional example of the invention the control electrodes 6 and energy absorbing electrodes 1 are not in the form of screens, but consist of openings in the walls of the resonator. In the centre of the tube there is an accelerating electrode 39 which consists of a cylinder the axis of which lies in the direction of the electron beam. An output loop for absorbing the high frequency power is located on the opposite side of the tube axis and is therefore not visible in the figure.

The several illustrated embodiments are indicative of the wide latitude in the design and construction of micro-wave generators embodying the invention and it is to be understood that other modifications which may occur to those familiar with the art fall within the spirit and scope of the invention as set forth in the following claims.

I claim:

1. A micro-wave generator comprising a single elongated hollow cavity resonator of substantially unobstructed uniform cross-section between two end walls, a pair of control electrodes at opposed walls of said hollow cavity resonator adjacent one of said end walls and spaced substantially from an anti-node of the electrical field established during operation of the generator, a pair of energy absorbing electrodes at opposite walls of said hollow cavity resonator and located closer to an anti-node of the electrical field than said control electrodes, means for developing an electron beam, and means for directing said electron beam through said pair of control electrodes and said pair of energy absorbing electrodes in series, the spacing and relative locations of said control electrodes and said energy absorbing electrodes being such that the feedback factor is less than unity.

2. A micro-wave generator as recitedin claim 1, wherein said hollow cavity resonator is of parallelepiped form.

3. A micro-wave generator as recited in claim 2, wherein means is provided for deflecting said electron beam through 180 in passage between said control electrodes and said energy absorbing electrodes.

4. A micro-wave generator as recited in claim 1, wherein said hollow cavity resonator comprises a tubular body of rectangular cross-section bent to position the several control and energy absorbing electrodes in alinement.

5. A micro-wave generator as recited in claim 4, wherein said hollow cavity resonator comprises a hollow body of J-shape.

6. A micro-wave generator as recited in claim 1, wherein said hollow cavity resonator is an annulus of rectangular cross-section with a wall extending radially across the annulus to provide a common wallfor the opposite ends of the clon gated hollowcavity resonator. v p

'7. A micro-wave generator as recited in.claim 4, wherein said electrodes are positioned in the circumferential walls of said hollow cavity resonator.

-8. A micro-wave generator as recited in claim 1, wherein said electrodes are'symmetrically arranged with respect to a medial plane of said hollow cavity resonator which is parallel to the path of the electron beam.

-9'.'A micro-wave generator as recited in claim 1, wherein said electrodes form parts of the walls of said hollow cavity resonator.

10. A micro-wave generator as recited in claim 1, wherein said energy absorbing electrodes are located at points at which the maximum alternating voltage is developed by said hollow cavity resonator.

11. A micro-wave generator as recited in claim 1, in combination with means at a point of maximum magnetic energy to vary the volume of said hollow cavity resonator to control the frequency of the generated micro-wave energy output.

12. A micro-wave generator as recited in claim 1, in combination with means at a point of maximum electrical energy to vary the volume of said hollow cavity resonator to control the frequency of the generated micro-wave energy output.

13. A micro-wave generator comprising an evacuated envelope, an electron gun and a collecting electrode within said envelope and adapted to establish a linear stream of electrons, an elongated hollow cavity resonator comprising an annulus of rectangular cross-section having diametrically located openings in the circumferential walls thereof to pass said linear electron stream, a wall extending radially across said annulus and closer to the pair of circumferential wall openings at the electron gun side of said annulus than to the other pair of circumferential wall openings, and coupling means extending into said annulus for connection to a load circuit.

14. A micro-wave generator as recited in claim 13, wherein said coupling means is a loop.

15. A micro-wave generator as recited in claim 13, wherein electrode means extend across and in the planes of the respective wall openings of said annulus.

16. In a micro-wave generator, the combination with an evacuated envelope, an elongated hollow cavity resonator of parallelepiped form within said envelope, an electron gun for establishing an electron stream, openings in opposite walls of said cavity resonator in line with said electron stream, and a second pair of openings in said opposite walls, of means for reversing the direction of travel of said electron stream to pass through said second pair of openings; said means comprising a collecting electrode and means creating a magnetic field.

17. In a micro-wave generator, an elongated hollow cavity resonator comprising inner and outer cylindrical walls cooperating with circular end plates to form an envelope, a radial wall extending between said inner and outer walls to constitute end closures for said elongated hollow cavity resonator, diametrically alined openings in said inner and outer cylindrical walls, the axis of said alined openings being at an acute angle to said radial wall, an electron gun in alinement with said openings, an electrode cooperating with said electron gun for establishing an electron stream through said openings, and means adjustable into the space between said inner and outer cylindrical walls to control the frequency of the micro-Wave energy developed by said generatorh y FRITZLITDI.

REFERENCES CITED p 7 The following references are of recordr in the file of this; patent:

' UNITED STATES PATENTS- Number Number 8 Name Date Llewellyn Jan. 23, 1945 Ryan Aug. 21, 1945 Pierce Feb. 5; 1946 Schelkunofi Aug. 13, 1946 Bowen Oct. 1, 1 946 Bowen; Oct. 14, 1947 Bowen -v Jan. 11; 1949 

